CN107911028A - A kind of DC DC converters of reload buffer device and the method for reducing reflux power - Google Patents

Abstract

The invention discloses a DC-DC converter equipped with a buffer and a method for reducing backflow power. A snubber capacitor is connected in parallel to each IGBT power switch tube of the DC-DC converter to form a snubber. Control the flow direction of power according to the power requirements on the left and right sides of the dual active bridge DC-DC converter, define the transmission power and return power, and adopt the double phase shift control method to control the soft power under different voltage ratio K Analyze and compare the switching conditions, calculate and optimize the transmission power limit and the optimal return power control program. In the control, the right return power is used to charge the inductor, and the left return power is used as the control target. The DC-DC converter of the method deploys a buffer on the power switch, which effectively improves the performance of the converter, suppresses overvoltage peaks, reduces EMI electromagnetic interference, and reduces the loss of the power switch tube. Compared with the existing single-phase-shift method, the return power of the converter is significantly reduced and stabilized by adopting the dual-phase-shift control method, which has wide application prospects and is easy to popularize.

Description

A DC-DC converter equipped with a buffer and a method for reducing backflow power

technical field

The invention relates to a DC-DC conversion electrical appliance, in particular to a double active bridge circuit DC-DC converter equipped with a buffer, which belongs to the category of power electronics and electric engineering.

Background technique

Dual active bridge (dual-active-bridge, DAB) DC-DC converter, that is, DC-DC converter, is functionally equivalent to two unidirectional DC-DC conversions, increasing the bidirectional flow capacity of energy, and Compared with the traditional unidirectional DC-DC converter, the number of components is saved, the volume of the system is reduced, the cost is reduced, and the efficiency of the system is improved at the same time. Therefore, the dual active bridge DC-DC converter has been more and more widely used in green energy such as DC motor drive, uninterruptible power supply, electric vehicle and wind power generation. The existing dual active bridge DC-DC converter, that is, the main circuit of the DC-DC converter is generally composed of active full bridges on the left and right sides, high-frequency transformers and inductors. The control method is mainly single-phase shift control, which is simple and easy to control. It is easy to realize, but the two-way flow effect of power and the ability to resist electromagnetic interference cannot meet the growing needs. Especially when the input and output voltages do not match or the voltage changes are relatively large, it is easy to generate backflow power and voltage spikes, increase the current stress, and increase the loss of the transformer.

Contents of the invention

The purpose of the present invention is to propose a DC-DC converter capable of suppressing voltage spikes and reducing electromagnetic interference (EMI) in view of the current situation that the existing dual active bridge DC-DC converter has a relatively large voltage change and the use effect is not good when the input and output voltages do not match. - The DC converter and its method for reducing the return power greatly reduce the return power of the dual active bridge DC-DC converter, and make the return power zero within a certain range. The method for reducing the backflow power of the present invention derives the relationship between shift phase and power based on a mathematical model, and adopts a double phase shift control strategy to effectively reduce the backflow power between loops.

The purpose of the present invention is achieved like this:

A DC-DC converter equipped with a buffer is characterized in that: the DC-DC converter includes active full bridges and high-frequency isolation transformers on the left and right sides, as well as inductors and resistors, and the active full bridges on both sides of the high-frequency isolation transformer are all It consists of four IGBT power switch tubes S ₁ ~ S ₈ , four diodes Q ~ ₁ Q ₈ and four snubber capacitors C ₁ ~ C ₈ , the diodes are connected in reverse series on the IGBT power switch tubes, and the snubber capacitors C ₁ ~ C ₈ are connected in parallel On the IGBT power switch tube; the four IGBT power switch tubes S ₁ ~ S ₄ of the active full bridge on the left are connected in reverse series with four diodes Q ₁ ~ Q ₄ , and four buffer capacitors C ₁ ~ C ₄ are connected in parallel, and the active full bridge on the right side The bridge consists of power switching tubes IGBTS ₅ ~ S ₈ in reverse series with four diodes Q ₅ ~ Q ₈ , and four buffer capacitors C ₅ ~ C ₈ in parallel; the transformation ratio of the high frequency isolation transformer T is n:1, and the inductance L is the external series inductance Add the sum of the leakage inductance of the transformer; the output voltage of the primary side is U _h1 , the input voltage of the secondary side is U _h2 , the inductor voltage is U _L , and the inductor current is i _L .

The switching tubes S ₁ to S ₈ on both sides of the left and right bridge-type DC converters have the same frequency, and the upper and lower switching tubes of each full bridge are complementary conduction; the switching tubes S ₁ , S ₄ and S ₂ of the left-side bridge-type DC converter , S ₃ are turned on in turn; the conduction law and switching frequency of the switching tubes S ₅ , S ₈ on the right side and S ₆ , S ₇ are the same as those on the left side.

There is a phase shift angle between the diagonal switching tubes of the full bridge on the left side of the DC-DC converter The phase shift within half a cycle is expressed as Among them, D ₁ is the internal shift phase; there is also a phase shift angle φ between the left U ₁ side and the DC-DC converter, and the phase shift within half a cycle is expressed as D ₂ = φ/π, where D ₂ For the shift-out comparison, the condition 0≤D ₁ ≤D ₂ ≤1 is satisfied.

The method of reducing the return power of the DC-DC converter with a buffer is to control the flow direction of power according to the power demand on the left side U ₁ side and the right side U ₂ side of the dual active bridge DC-DC converter. Define transmission power and return power, adopt double phase-shift control method, analyze and compare the soft switching conditions under different voltage ratio K, calculate and optimize the limit of transmission power. Including the following steps:

(1) By analyzing the working mode of the dual active bridge DC-DC converter, the ideal working waveform diagram of the converter is drawn;

(2) Carry out theoretical calculations according to the drawn working waveform diagram, and calculate the inductor current value at each moment;

(3) Calculate the mathematical expressions of the transmission power and the return power with respect to the phase shift angle according to the definition of the transmission power and the return power;

(4) according to the inductance current value obtained in step (2), obtain the soft switching condition of the double active bridge DC-DC converter;

(5) Substituting the soft switching condition obtained in the step (4) into the return power expression obtained in the step (3), calculate the limit of the transmission power at this time, within this limit, the theoretical value of the return power is zero;

(6) When the transmission power is outside the limit sought in (5), utilize Lagrangian number multiplication to solve the optimal point of return power;

(7) Finally, it is verified by simulation analysis.

The phase shift angle is defined as: there is a phase shift angle between the full-bridge diagonal switch tubes on the left side of the DC-DC converter The phase shift within half a cycle is expressed as Among them, D ₁ is the internal shift phase; there is also a phase shift angle φ between the left U ₁ side and the right U ₂ side, and the phase shift within half a cycle is expressed as D ₂ = φ/π, where D ₂ For outward shifting, the condition 0≤D ₁ ≤D ₂ ≤1 is satisfied;

The definition of backflow power is: when the voltage U _h1 on the left side of U ₁ is opposite to the direction of the inductor current i _L , the energy stored in the inductor flows back to the side of U ₁ , this part of the power is the backflow power, at time t ₁ to t ₁ ' The reflux power is defined as the left reflux power; when the voltage U _h2 on the right U ₂ side is in the opposite direction to the inductor current i _L , the energy stored in the inductor flows back to the U ₂ side, and the reflux power at time t ₄ -t' ₄ is defined as The return power on the right side; the return power on the right side of the H-bridge (U ₂ side) is used to charge the inductor, and the return power on the left side of the H-bridge (U ₁ side) is used as the control target.

According to step (1), calculate the inductor current value i _L at each moment under the dual phase-shift control by drawing the ideal working waveform diagram of the converter:

Let t ₀ =0, we can get t ₁ =D ₁ T _hs , t ₂ =D ₂ T _hs , t ₃ =T _hs , t ₄ =(1+D ₁ )T _hs , t ₅ =(1+D ₂ )T _hs , t ₆ =2T _hs , where T _hs is half a switching cycle; assuming voltage regulation ratio k=U ₁ /nU ₂ , switching frequency f=1/2T _hs , by symmetry i _L (t ₀ )= -i _l (t ₃ ), i _L (t ₁ )＝-i _L (t ₄ ), i _L (t ₂ )＝-i _L (t ₅ ) can get:

In step (3), according to the definition of transmission power and return power, calculate the mathematical expressions of transmission power and return power with respect to the phase shift angle as follows: According to the solution of the power formula

Know the solution definition of the power in one cycle of the inductance

The transmission power P _D under double phase shift control can be obtained as:

According to the definition of reflux power, the reflux power under double phase shift can be obtained as:

Among them, P _{Dcir_l} is the return power of the left H-bridge, and P _{Dcir_r} is the return power of the right H-bridge.

In step (4), according to the inductor current value obtained in step (2), the soft switching condition of the dual active bridge DC-DC converter is analyzed:

Define i _L (t ₁ ) = 0 as the critical condition of soft switching. According to formula (2), when the inductor current satisfies i _L (t ₁ )≤0, the switch tubes S ₁ and S ₄ of the left H-bridge realize Zero-voltage conduction and soft-switching turn-off, according to the symmetry of the inductor current, the switch tubes _S2 and _S3 can also achieve zero-voltage conduction and soft-switching turn-off; the soft-switching constraints of the left H-bridge can be obtained:

For the same reason, the inductor current i _L (t ₂ )≥0 at time t ₂ represented by formula (3), the constraint condition for the soft switching of the right H-bridge is:

At this time, the right H-bridge switch tubes S ₅ -S ₈ all meet the zero-voltage turn-on and soft-switch turn-off conditions.

In step (5), substitute the soft switching condition obtained in step (4) into the return power expression obtained in step (3), and calculate the limit of the transmission power at this time. Within this limit, the theoretical value of the return power is zero:

The transmission power is per unitized, and the maximum transmission power P _N under the traditional single phase shift control is taken as the reference value, then:

According to equations (4) and (5) and equation (10), the transmission power and left and right sides under double phase shift control can be obtained

The per unit value of the return power is:

The minimization of the left return power is:

Substituting soft switching critical condition (7) into formula (11) can get:

From formula (14), it can be seen that when the transmission power When , the return power at this time is theoretically zero; when the transmission power At this time, there is no solution to equation (14), and the optimal reflux power operating point is (D ₁ , D ₂ ), which is determined by Lagrangian multiplication: Equation (15) is the basic form of Lagrangian multiplication:

L(x,y,λ)=f(x,y)+λg(x,y) (15)

Where f(x,y) is the objective function, g(x,y) is the constraint condition that restricts the objective function, λ is the Lagrangian multiplier; the return power is used as the objective function, and the transmission power condition is the equality constraint The conditional function of , formula (15) is rewritten as the following equation:

L(D ₁ ,D ₂ ,λ)＝P _D ' _cir (D ₁ ,D ₂ )+λ(P ₀ -P) (16)

Depend on Available:

Therefore, the minimum return power can be obtained:

The optimal control process to reduce the return power is:

Step 1: Sampling output voltage U ₂ , output current i ₂ and input voltage U ₁ to determine output power P and transformer conversion ratio k;

Step 2: Determine whether the relationship between the output power P and k satisfies Yes, go to the third step; No, go to the fourth step;

The third step: determine the phase shift angle

Step 4: Determine the phase shift angle

Step 5: Generate a PWM pulse to turn on the switch tube according to the determined D ₁ .

The positive effect of the present invention is:

1. The DC-DC converter of the present invention deploys a buffer on the power switch, and the buffer capacitors C ₁ to C ₈ effectively improve the performance of the converter, suppress overvoltage peaks, reduce EMI electromagnetic interference, and reduce the loss of the power switch tube. Appropriate equipment is provided for reducing return power.

2. The present invention derives the relationship between the shift ratio and power based on a mathematical model, adopts a double phase shift control method, analyzes and compares the soft switching conditions under different voltage ratios K, calculates and optimizes the limit of the transmission power, Through simulation verification, the invention has a certain degree of improvement compared with the prior art. When transmitting power When , the return power is theoretically zero, when the transmission power When , the return power is not zero, but the optimal return power operating point can be obtained at this time, which is of positive significance in practical application.

3. The structure of the DC-DC converter buffer is simple and reliable, and the cost is low. The method of controlling the loop power has practical guiding significance. It has a very wide application prospect for the current increasing DC-DC converter application demand and is easy to promote.

Description of drawings

Fig. 1 is a schematic diagram of a conventional DAB converter.

Fig. 2 is a schematic structural diagram of the DC-DC converter of the present invention.

Fig. 3 is a working waveform diagram of the DC-DC converter of the present invention.

Fig. 4 is a comparison chart of the return power under the single phase shift control of the prior art and the double phase shift control of the present invention.

In the figure, the abscissa P is the per unit value of the transmission power, and the ordinate P _cir is the per unit value of the return power. The dotted line is the change curve of the return power with the transmission power under double phase-shift control. The different voltage ratios K, the solid line It is the change curve of the return power and the transmission power under single phase shift control, and its different voltage transformation ratio K.

Fig. 5 is a schematic diagram of the method for reducing the DC-DC converter of the present invention.

Fig. 6 is an optimal control program diagram for reducing backflow in the present invention.

FIG. 7 is a waveform diagram of output power when the load is 64Ω under single phase shift control in the prior art.

Fig. 8 is a waveform diagram of the output power when the load is 64Ω when the DC-DC converter equipped with a buffer and the double phase-shift control method of the present invention are adopted.

FIG. 9 is a waveform diagram of output power when the load is 140Ω under single phase shift control in the prior art.

Fig. 10 is a waveform diagram of the output power when the load is 140Ω by adopting the DC-DC converter equipped with a buffer and the double phase-shift control method of the present invention.

In the figure, S ₁ to S ₈ are IGBT power switch tubes, Q ₁ to Q ₈ are diodes of reverse series power switch tubes, C ₁ to C _{8 are} buffer capacitors connected in parallel to the IGBT power switch tubes to form a buffer, and T is For a high-frequency isolation transformer with a transformation ratio of n:1, the inductance L is the sum of the external series inductance plus the leakage inductance of the transformer; the output voltage on the primary side is U _h1 , and the input voltage on the secondary side is U _h2 .

Detailed ways

See accompanying drawings 1 and 2.

The DC-DC converter includes a high-frequency isolation transformer, DC active full bridges and inductors on the left and right sides.

In order to improve the performance of the converter, the present invention deploys a buffer circuit on the power switch. The main function of the buffer circuit is to suppress overvoltage, reduce the loss of the power switch tube, suppress voltage spikes and effectively reduce EMI electromagnetic interference. DC-DC converter with buffer, active full bridge high frequency isolation transformer The active full bridge on both sides is composed of four IGBT power switch tubes, four diodes and four snubber capacitors, and the diodes are connected in reverse series to the IGBT power On the switch tube, the snubber capacitor is connected in parallel to the IGBT power switch tube. Four IGBT power switch tubes S ₁ ~ S ₄ of the active full bridge on the left are connected in reverse series with four diodes Q ₁ ~ Q ₄ , and four buffer capacitors C ₁ ~ C ₄ are connected in parallel. The active full bridge on the right side is composed of power switch tubes IGBT S _{5 ~} ~ S ₈ connect four diodes Q ₅ ~ Q ₈ in reverse series, and connect four buffer capacitors C ₅ ~ C ₈ in parallel.

In this embodiment, two load resistors of the DC-DC converter are selected, 64Ω and 140Ω, and the value of the selected buffer capacitor is: C=100nF.

The transformation ratio of the high-frequency isolation transformer T is n:1, the inductance L is the sum of the external series inductance plus the leakage inductance of the transformer; the output voltage of the primary side is U _h1 , the input voltage of the secondary side is U _h2 , the inductance voltage is U _L , and the inductance The current is i _L .

The switching tubes S ₁ to S ₈ on both sides of the left and right bridge-type DC converters have the same frequency, and the upper and lower switching tubes of each full bridge are complementary conduction; the switching tubes S ₁ , S ₄ and S ₂ of the left-side bridge-type DC converter , S ₃ are turned on in turn; the conduction law and switching frequency of the switching tubes S ₅ , S ₈ on the right side and S ₆ , S ₇ are the same as those on the left side.

There is a phase shift angle between the diagonal switch tubes of the H-bridge on the left side of the DC-DC converter The phase shift within half a cycle is expressed as Among them, D ₁ is the internal shift phase; there is also a phase shift angle φ between the left U ₁ side and the DC-DC converter, and the phase shift within half a cycle is expressed as D ₂ = φ/π, where D ₂ For the shift-out comparison, the condition 0≤D ₁ ≤D ₂ ≤1 is satisfied.

See accompanying drawings 3 and 5.

Accompanying drawing 5 has provided the method for reducing backflow power of the present invention. In the figure, PI is the output power of the PI regulator as P.

Control the flow direction of power according to the power demand on the left U ₁ side and right U ₂ side of the dual active bridge DC-DC converter, define the transmission power and return power, and adopt the double phase shift control method to control different voltages Analyze and compare the soft switching conditions under the transformation ratio K, calculate and optimize the limit of transmission power; including the following steps:

(1) By analyzing the working mode of the dual active bridge DC-DC converter, the ideal working waveform diagram of the converter is drawn;

(2) Carry out theoretical calculations according to the drawn working waveform diagram, and calculate the inductor current value at each moment;

(3) Calculate the mathematical expressions of the transmission power and the return power with respect to the phase shift angle according to the definition of the transmission power and the return power;

(4) according to the inductance current value obtained in step (2), obtain the soft switching condition of the double active bridge DC-DC converter;

(5) Substituting the soft switching condition obtained in the step (4) into the return power expression obtained in the step (3), calculate the limit of the transmission power at this time, within this limit, the theoretical value of the return power is zero;

(6) When the transmission power is outside the limit sought in step (5), utilize Lagrangian number multiplication to solve the optimal point of return power;

(7) Finally, through simulation analysis.

The phase shift angle is defined as: there is a phase shift angle between the full-bridge diagonal switch tubes on the left side of the DC-DC converter The phase shift within half a cycle is expressed as Among them, D ₁ is the internal shift phase; there is also a phase shift angle φ between the left U ₁ side and the right U ₂ side, and the phase shift within half a cycle is expressed as D ₂ = φ/π, where D ₂ For outward shifting, the condition 0≤D ₁ ≤D ₂ ≤1 is satisfied;

From the working waveform diagram of the DC-DC converter given in Figure 3, it can be seen that the return power is defined as: when the left H bridge, _U1 side voltage U _h1 and the inductor current i _L are in opposite directions, the energy stored in the inductor flows back To the U ₁ side, this part of the power is the backflow power, and the backflow power at the time t ₁ ~ t ₁ ' is defined as the left side backflow power; when the right side of the H bridge, that is, the U ₂ side voltage U _h2 and the inductor current i _L are in opposite directions, at this time The energy stored in the inductor flows back to the U ₂ side, and the reflux power at time t ₄ -t' ₄ is defined as the right reflux power; the right H bridge, that is, the U ₂ side reflux power, is used to charge the inductor; the left H bridge, that is, U Side ₁ backflow power is used as the control target.

Calculate the inductor current value i _L at each moment under the dual phase-shift control through the drawn ideal working waveform diagram of the converter according to step (1).

Let t ₀ =0, we can get t ₁ =D ₁ T _hs , t ₂ =D ₂ T _hs , t ₃ =T _hs , t ₄ =(1+D ₁ )T _hs , t ₅ =(1+D ₂ )T _hs , t ₆ =2T _hs , where T _hs is half a switching cycle; assuming voltage regulation ratio k=U ₁ /nU ₂ , switching frequency f=1/2T _hs , by symmetry i _L (t ₀ )= -i _l (t ₃ ), i _L (t ₁ )＝-i _L (t ₄ ), i _L (t ₂ )＝-i _L (t ₅ ) can get:

In step (3), according to the definition of transmission power and return power, calculate the transmission power and return power

The mathematical expression about the phase shift angle is as follows:

according to The transmission power P _D under double phase shift control can be obtained as:

According to the definition of reflux power, the reflux power under double phase shift can be obtained as:

Among them, P _{Dcir_l} is the return power of the left H-bridge, and P _{Dcir_r} is the return power of the right H-bridge. According to the operating principle of the dual active bridge DC-DC converter, the return power of the left H-bridge is sent back to the voltage source, and the low-value return power of the right H-bridge is used to charge the inductor. So return power on the left is usually the last thing people expect. In this method the main focus is on the control to minimize the left return power.

In step (4), according to the inductor current value obtained in step (2), the soft switching condition of the dual active bridge DC-DC converter is analyzed:

Define i _L (t ₁ ) = 0 as the critical condition of soft switching. According to formula (2), when the inductor current satisfies i _L (t ₁ )≤0, the switch tubes S ₁ and S ₄ of the left H-bridge realize Zero-voltage conduction and soft-switching turn-off, according to the symmetry of the inductor current, the switch tubes _S2 and _S3 can also achieve zero-voltage conduction and soft-switching turn-off; the soft-switching constraints of the left H-bridge can be obtained:

For the same reason, the inductor current i _L (t ₂ )≥0 at time t ₂ represented by formula (3), the constraint condition for the soft switching of the right H-bridge is:

At this time, the right H-bridge switch tubes S ₅ -S ₈ all meet the zero-voltage turn-on and soft-switch turn-off conditions.

In step (5), substitute the soft switching condition obtained in step (4) into the return power expression obtained in step (3), and calculate the limit of the transmission power at this time. Within this limit, the theoretical value of the return power is zero:

The transmission power is per unitized, and the maximum transmission power P _N under the traditional single phase shift control is taken as the reference value, then:

According to formulas (4) and (5) and formula (10), the per unit values of transmission power and left and right return power under double phase shift control can be obtained as:

The minimization of the left return power is:

Substituting soft switching critical condition (7) into formula (11) can get:

From formula (14), it can be seen that when the transmission power When , the return power at this time is theoretically zero; when the transmission power At this time, there is no solution to equation (14), and the optimal reflux power operating point is (D ₁ , D ₂ ), which is determined by Lagrangian multiplication: Equation (15) is the basic form of Lagrangian multiplication:

L(x,y,λ)=f(x,y)+λg(x,y) (15)

Where f(x,y) is the objective function, g(x,y) is the constraint condition that restricts the objective function, λ is the Lagrangian multiplier; the return power is used as the objective function, and the transmission power condition is the equality constraint The conditional function of , formula (15) is rewritten as the following equation:

L(D ₁ ,D ₂ ,λ)=P' _Dcir (D ₁ ,D ₂ )+λ(P ₀ -P) (16)

Depend on Available:

Therefore, the minimum return power can be obtained:

See accompanying drawing 6.

The control flow of the optimal algorithm to reduce the backflow power of the DC converter is:

Step 1: Sampling output voltage U ₂ , output current i ₂ and input voltage U ₁ to determine output power P and transformer conversion ratio k;

Step 2: Determine whether the relationship between the output power P and k satisfies Yes, go to the third step; No, go to the fourth step;

The third step: determine the phase shift angle

Step 4: Determine the phase shift angle

Step 5: Generate a PWM pulse to turn on the switch tube according to the determined D ₁ .

See attached drawing 4.

Fig. 4 is a comparison chart of the return power under the single phase shift control of the prior art and the double phase shift control of the present invention. In the figure, the abscissa P is the per unit value of the transmission power, and the ordinate P _cir is the per unit value of the return power. The dotted line is the change curve of the return power with the transmission power under double phase-shift control. The different voltage ratios K, the solid line It is the change curve of the return power and the transmission power under single phase shift control, and its different voltage transformation ratio K. It can be seen from the figure that under the same conditions, the return power of the converter using the buffer-installed DC-DC converter of the present invention and its double phase-shifting method is significantly smaller than that of the converter in the prior art.

The converter backflow power waveform diagrams verified by simulation experiments in the present invention are shown in accompanying drawings 7, 8, 9 and 10.

Figure 7 shows the output power waveform when the load resistance is 64Ω when the single phase shift control method is adopted. It can be seen from the figure that the return power is about P _cir =2000W. Fig. 8 is a power waveform diagram when the load resistance is 64Ω using the converter of the present invention and the double phase-shifting method. At this time, the output power is P=2500W, and the per unit value of the output power is P ₀ =0.8333>0.8. At this time, the theoretical value of the return power is not zero. It can be seen from Figure 8 that the return power at this time is about P _Dcir =500W . Compared with the prior art single phase shifting method in Fig. 7, the return power is greatly reduced.

Fig. 9 is the output waveform when the load resistance is 140Ω when the single phase shift control method is adopted. It can be seen from the figure that the return power is about P _cir =900W. Fig. 10 is the output power waveform when the load resistance is 140Ω using the converter and the double phase-shift control method of the present invention. The output power P=1142.86W, the rated power of the converter is P=3000W, the per unit value of the output power is P ₀ =0.381<0.8, and the theoretical value of the backflow power is zero at this time. It can be seen from Figure 10 that the backflow power is zero, which is consistent with the theoretical analysis and reaches an ideal state.

It can be seen from the waveform diagram that by adopting the DC-DC converter and the double phase-shift control method of the present invention, the return power of the converter is significantly reduced and stabilized.

The present invention deduces the relationship between shift phase and power based on a mathematical model, adopts a double phase shift control strategy, and effectively reduces the backflow power between loops. When transmitting power , the return power is theoretically zero, when the transmission power When , the reflux power is not zero, and the optimal reflux power operating point at this time is obtained as:

.

Claims (9)

1. A kind of 1. DC-DC converter of reload buffer device, it is characterised in that：DC-DC converter containing the active full-bridge of the right and left and High-frequency isolation transformer and inductance, resistance, the active full-bridge on high-frequency isolation transformer both sides is by four IGBT power switch Manage (S₁~S₈), four diode (Q₁~Q₈) and four buffering capacitance (C₁~C₈) composition, diode is played a reversed role to be opened in IGBT power Close on pipe, buffer capacitance (C₁~C₈) be connected in parallel on IGBT power switch pipes；Left side four IGBT power switch pipes of active full-bridge (S₁~S₄) play a reversed role four diode (Q₁~Q₄), four buffering capacitances (C in parallel₁~C₄), the active full-bridge in right side is by power switch Pipe IGBT (S₅~S₈) play a reversed role four diode (Q₅~Q₈), four buffering capacitances (C in parallel₅~C₈)；High-frequency isolation transformer T's No-load voltage ratio is n：1, inductance L add the sum of transformer leakage inductance for outer string inductance；Primary side output voltage is U_h1, secondary side input voltage is U_h2, inductive drop U_L, inductive current i_L。
2. 2. the DC-DC converter of reload buffer device as claimed in claim 1, it is characterised in that：Two bridge-types in the left and right are straight Current converter both sides switching tube (S₁~S₈) frequency is identical, the complementary conducting of switching tube up and down of each full-bridge；Left side bridge-type direct current becomes Switching tube (the S of parallel operation₁、S₄) and (S₂、S₃) turn in turn；Switching tube (the S on right side₅、S₈) and (S₆、S₇) conducting rule, switch Frequency is identical with left side.
3. 3. the DC-DC converter of reload buffer device as claimed in claim 1 is straight, it is characterised in that：It is complete on the left of DC-DC converter There are a phase shifting angle between the diagonal switching tube of bridgePhase shift ratio in half period is expressed asWherein D₁For interior shifting Compare；Left side U₁Side and the right U₂There is also a phase shifting angle φ between side, the phase shift ratio in half period is expressed as D₂=φ/ π, wherein D₂For outer phase shift ratio, meet 0≤D of condition₁≤D₂≤1。
4. 4. a kind of method that DC-DC converter using reload buffer device as claimed in claim 1 reduces reflux power, it is special Sign is：The U on the left of double active bridge DC-DC converters₁Side and right side U₂Side both sides control the demand of power the stream of power Dynamic direction, defines transimission power, reflux power, using two-track phase control method, to the Sofe Switch condition under different voltages no-load voltage ratio K Analysis comparison is carried out, calculates and preferably go out the boundary of transimission power；Include the following steps：

   (1) by analyzing the operating mode of double active bridge DC-DC converters, the ideal operation oscillogram of converter is drawn out；

   (2) according to the working waveform figure drawn, theoretical calculation is carried out, calculates the inductor current value at each moment；

   (3) according to the definition of transimission power and reflux power, the mathematics of transimission power and reflux power on phase shifting angle is calculated Expression formula；

   (4) according to step (2) obtained inductor current value, the Sofe Switch condition of double active bridge DC-DC converters is drawn；

   (5) required Sofe Switch condition in step (4) is substituted into required reflux power expression in step (3), calculates and pass at this time The boundary of defeated power, in this boundary, the theoretical value zero for the power that flows back；

   (6) when transimission power is when outside boundary required by (5), lagrange multiplier approach is utilized to solve reflux power optimized point；

   (7) verified finally by simulation analysis.

   The definition of phase shifting angle is：There are a phase shifting angle between the diagonal switching tube of full-bridge on the left of DC-DC converterHalf period Interior phase shift ratio is expressed asWherein D₁For interior phase shift ratio；Left side U₁Side and right side U₂There is also a phase shift between side Angle φ, the phase shift ratio in half period are expressed as D₂=φ/π, wherein D₂For outer phase shift ratio, meet 0≤D of condition₁≤D₂≤1；

   Reflux power definition be：As left side H bridges, that is, U₁Side voltage U_h1With inductive current i_LDirection in inductance on the contrary, store at this time Energy be back to U₁Side, this Partial Power for reflux power, t₁~t₁' the moment reflux power definition for left side flow back power；When Right side H bridges, that is, U₂Side voltage U_h2With inductive current i_LDirection is on the contrary, the energy stored at this time in inductance is back to U₂Side, t₄-t'₄ Moment reflux power definition is right side reflux power；Right side H bridges, that is, U₂It is induction charging that side reflux power, which is used for,；With left side H bridges That is U₁Side reflux power is as control targe.
5. 5. the method as claimed in claim 4 for reducing reflux power, it is characterised in that：According to step (1) by drawing out Converter ideal operation oscillogram, calculate the inductor current value i for calculating each moment under dual phase shifting control_L：Make t₀=0, can Obtain t₁=D₁T_hs, t₂=D₂T_hs, t₃=T_hs, t₄=(1+D₁)T_hs, t₅=(1+D₂)T_hs, t₆=2T_hs, wherein T_hsFor half of switch Cycle；If voltage, which is adjusted, compares k=U₁/nU₂, switching frequency f=1/2T_hs, by symmetry i_L(t₀)=- i_l(t₃), i_L(t₁)=- i_L (t₄), i_L(t₂)=- i_L(t₅) can obtain：

   。
6. 6. the method as claimed in claim 4 for reducing reflux power, it is characterised in that：In step (3), according to transimission power With the definition of reflux power, calculate transimission power and reflux power is as follows on the mathematic(al) representation of phase shifting angle：According to solution Horse-power formula

   Know the solution definition of inductance a cycle internal power

   The transimission power P under dual phase shifting control can be obtained_DFor：

   According to the definition of reflux power, the reflux power that can be obtained under dual phase shift is：

   Wherein, it is P_{Dcir_l}For the reflux power of left side H bridges, P_{Dcir_r}For right side H bridges reflux power.
7. 7. the method as claimed in claim 4 for reducing reflux power, it is characterised in that：In step (4), according to step (2) Obtained inductor current value, analyzes the Sofe Switch condition of double active bridge DC-DC converters：

   Define i_L(t₁It is Sofe Switch critical condition during)=0, is known by formula (2), when inductive current meets i_L(t₁During)≤0, left side H The switching tube S of bridge₁And S₄Realize that no-voltage conducting is turned off with Sofe Switch, according to the symmetry of inductive current it is recognised that switching tube S₂And S₃It can equally realize no-voltage conducting and Sofe Switch shut-off；It can obtain left side H bridge Sofe Switch constraintss：

   The t represented with reason formula (3)₂Moment inductive current i_L(t₂) >=0, right side H bridge Sofe Switch constraintss are：

   Right side H bridge switch pipes S at this time₅~S₈It is satisfied by no-voltage conducting and Sofe Switch turn-off criterion.
8. 8. the method as claimed in claim 4 for reducing reflux power, it is characterised in that：In step (5),

   Required Sofe Switch condition in step (4) is substituted into required reflux power expression in step (3), calculates and transmits work(at this time The boundary of rate, in this boundary, the theoretical value zero for the power that flows back：

   By transimission power standardization, the maximum transmission power P under traditional single phase shifting control is taken_NOn the basis of be worth, then have：

   According to formula (4) and (5) and formula (10), transimission power under dual phase shifting control and left and right side reflux power can be obtained Perunit value is：

   Left side reflux power is minimised as：

   Sofe Switch critical condition (7), which is brought into formula (11), to be obtained：

   From formula (14), work as transimission powerWhen, it is zero in reflux Power Theory at this time；

   Work as transimission powerWhen, for this up-to-date style (14) without solution, optimal reflux power operating point is (D₁,D₂), use glug Bright number of days multiplication determines：Formula (15) is the citation form of lagrange multiplier approach：

   L (x, y, λ)=f (x, y)+λ g (x, y) (15)

   Wherein f (x, y) is object function, and g (x, y) is to restrict bound for objective function, and λ is Lagrange's multiplier；

   Using the power that flows back as object function, the conditional function using transimission power condition as equality constraint, formula (15) is rewritten For equation below：

   L(D₁,D₂, λ) and=P'_Dcir(D₁,D₂)+λ(P₀-P) (16)

   ByIt can obtain：

   Therefore minimum reflux power can be obtained：

   。
9. 9. the method as claimed in claim 4 for reducing reflux power, it is characterised in that：Reduce the optimum control stream of reflux power Cheng Wei：

   The first step：Sampling and outputting voltage U₂With output current i₂And input voltage U₁, determination power output P and transformer are changed Compare k；

   Second step：Judge whether the relation between output power P and k meetsIt is, into the 3rd step；It is no, into Enter the 4th step；

   3rd step：Determine phase shifting angle

   4th step：Determine phase shifting angle

   5th step：According to definite D₁Produce pwm pulse conducting switching tube.